Hi Keith.

It depends also on what is your budget.

I think that Moi is a wanderful tool suitable for working on many different kind of projects.

But you also should keep in mind that is lacks some very important features when it comes to managing stuff for "building".

For example first of all History.

Moi is not a classical "history based" cad.
When you have to simply modify for example the length of an object that represent a "wooden board" on which you have already applied a fillet or chamfer,
you have to do all the operation manually. Delete the fillet, repair the surface, modify the lenght, redo the fillet. Often the fastest thing in Moi is to redo the complete object from scratch.

Also Moi doesn't have an effective "Annotation and dimension" toolset.

You have to consider these things if you want your son to study on a "industry standard" tool.

You would obtain great result for example if you couple Moi with Rhino.

Ciao!